Name: _______________________________ Date: ___________________

6.1 - MeiosisObjectives

• Describe the process of meiosis, Compare and contrast meiosis and

mitosis, Explain why meiosis is needed

Meiosis

• _______________________________– 2 parents – genetic differences

• The process of Meiosis results in the production of special cells called ____________________________

• Gametes have ______________the number of chromosomes as body cells

• Cell division _________________________ in Meiosis

• Once at the end of Meiosis I and again at the end of Meiosis II

• In Meiosis I, _________________________ chromosomes called ________________________

chromosomes separate

• In Meiosis II, ______________________________ separate

• The process of meiosis shuffles genetic information and results in variation of the gametes

• Results in _______________________

Important Terms

• ___________________: half the total number of chromosomes found in gametes (in humans = 23)

• ___________________: total number of chromosomes found in body cells (in humans = 46)

Meiosis

• AKA: Germ cell division or sex cell division

• Purpose: to produce gametes (i.e. sex cells:_________________ and _________________ )

• Products: _________________________ each genetically _____________________ this creates

genetic variability

Fertilization

• 2 gametes come together; in humans an egg and sperm come together

• Each has _______ chromosomes, thus together there are _____ in the zygote

Meiosis: Reducing Chromosome Number

Meiosis: Chromosome Number Sequence

Meiosis – Prophase I

Parent

All genetically

• Chromosomes coil and become visible.

• Nuclear membrane ______________________ & Spindle fibers form.

• ___________________________ chromosomes move towards each other and pair.

Meiosis – Metaphase I

• _____________ of homologous chromosomes move to the ___________ of the

cell.

• These pairs are aligned on either side of the metaphase plate.

Meiosis – Anaphase I

• _________________________ chromosome _________ are pulled ____________

from each other towards opposite ends of the cell. Paired chromatids

remain__________________.

Meiosis - Telophase I

• Paired chromatids may uncoil and become less visible.

• Nuclear membranes may form around each chromosome cluster.

• Spindle fibers _______________________ and ____________________ occurs.

Meiosis II

• Phase II of meiosis is the __________________________________________ of haploid cells.

• Although there will be _____________________________________________ cells at the end of meiosis

II, all other processes for this division are similar to mitosis.

Meiosis II – Prophase II

• Paired chromatids coil.

• Spindle fibers form

• Nuclear membrane disappears.

Meiosis II – Metaphase II

• Paired chromatids __________________ in the middle of the cell.

• The ____________________________ are attached to spindle fibers.

Meiosis II – Anaphase II

• Each pair of chromatids split at the ________________ to form two ____________

______________________________.

• Chromosomes move to opposite ends of the cell.

Meiosis II – Telophase II

• Chromosomes uncoil and become less visible

• _______________________________ form around _______________________

• Spindle fibers disappear

• Cytokinesis occurs.

Meiosis - Cytokinesis

• Same process as in mitosis

• Four ___________________________ cells are formed.

• These cells are called haploid cells (n).

• # chromosomes = ___________________________ of chromosomes of parent

cell.

Meiosis Events:

Meiosis I

• Matching chromosome pairs (homologous chromosomes) move to

opposite poles of the cell - two daughter cells result.

Meiosis II

• Chromatids of each chromosome are pulled apart - the end result is four haploid cells, each with half

the number of chromosomes. These develop into gametes.

Crossing Over

• Important event that occurs _______________________

each chromosome pair in meiosis I

• There is an ______________________________ of

segments of ________________________ and picks up

new genetic information

Independent Assortment:

• This occurs when homologous pairs of chromosomes _________________________ at the equator and

move towards opposite poles of the cell.

Fertilization

• There are more than _____________ combinations possible for these 23 pairs in any egg or sperm cell

• When fertilization occurs, ________________________________ different zygotes are possible from

the combination of one sperm cell and one egg cell!

Gamete Formation

• Males produce ____________________ for every round of meiosis

• Females produce ____________________________ for each round of meiosis: 3 of the 4 “eggs”

produced die off - called polar bodies

• All the cytoplasm, nutrients and energy gets put into one egg

Chromosome Mutations

• Sometimes occur spontaneously

• Chromosome changes during meiosis can cause changes in the genetic information.

• Parts of chromosomes can be inverted, _________________________, duplicated or

___________________to another spot.

Occur because of mutagens

• Chromosome changes, sometimes leading to genetic disease or death, can be caused by mutagens such as

radiation or chemicals.

Can occur if there is failed separation of chromosomes in meiosis

• Failed separation means that a gamete may end up with _______ chromosome or ________________ of a

chromosome.

• Zygotes that result from these gametes rarely survive, and if they do, they will have serious genetic

disorders.

Diagnosing Genetic Disorders

• A geneticist can prepare a different type

of picture for individuals that show

all chromosomes called ______________________________

• By analyzing karyotypes, geneticists can determine whole chromosome mutations

• Can diagnose genetic disorders or syndromes

• Down syndrome – most frequent genetic disorder - Caused by an extra ________________ chromosome

Meiosis Overview